1. Field of the Invention
This invention relates to the fabrication of devices and, in particular, the fabrication of devices involving lithographic procedures.
2. Art Background
Lithographic techniques are widely practiced in the manufacture of devices such as semiconductor devices. These techniques rely on a mask material that is deposited on a substrate, delineated into a specific pattern, and subsequently utilized to form a particular device structure. (Substrate, for the purposes of this disclosure, is a body, e.g., a semiconductor body, that is being processed into a device, e.g., a semiconductor device. This body could include not only semiconductor materials or optoelectronic materials, but also regions of organic materials, metals, and dielectrics.) Often a mask material to be adequate for a specific application is required to have several distinct chemical properties. (A chemical property, for purposes of this disclosure, is a property that depends on the reactivity or lack of reactivity of a composition under the influence of heat, radiation, and/or chemical agents. Reactivity in this context includes decomposition.)
An example of an application requiring multiple properties involves a contemplated bilevel resist including (1) a lower layer that contacts the substrate and that is susceptible to removal by contact with an oxygen reactive ion etching (RIE) environment and (2) an upper layer overlying this lower layer that is lithographically defined but essentially unaffected, relative to the lower layer, by oxygen RIE, i.e., etches in an RIE oxygen environment at a rate at least 5 times, preferably 10 times, less than the lower layer. In use, the upper layer is lithographically defined, and the exposed regions of the lower layer are then removed by interaction with an oxygen RIE environment. Because the upper layer is oxygen RIE resistant, it is not substantially removed during the removal of the exposed regions of the lower layer. Thus, an exemplary multiple property lithographic material is a composition that is both lithographically definable by exposure to a nominal dose of radiation, e.g., electromagnetic radiation, and also oxygen RIE resistant. Although materials have been developed that satisfy these two requirements, such development is quite difficult and only a limited number of satisfactory materials has been found.
Similarly, there are many other materials required for lithography which, because of specific use parameters, have extremely demanding chemical property requisites. A unified approach to developing such materials has not been found and, indeed, often materials satisfying combined chemical property requirements are not forthcoming.